1. Field of the Invention
The present invention relates to a sensor mounted on an intra-corporeal medical device. More particularly, the present invention relates to a sensor mounted on the distal end of a catheter for detecting pressure acting thereon.
2. Description of the Related Art
Catheters and endoscopes are medical devices that are inserted into passageways in the human body such as blood vessels to perform medical treatment. These devices typically include a tube, which is inserted into the body, and a manipulator for manipulating the tube from outside the patient's body. The tube is inserted into an intra-corporeal passageway, such as a blood vessel. Then, the doctor uses the manipulator to guide the distal end of the tube to a desirable point, where he or she performs measuring (e.g., measurement of the blood pressure) or medical treatment (e.g. vasodilation).
The intra-corporeal passageways are curved and branched and their diameters vary at different locations. In addition, obstacles such as a thrombus may narrow the passageways. The doctor therefore uses the manipulator to bend the tube in order to guide the tube's distal end through branches.
When operating a prior art catheter, the doctor senses an increase in the insertion resistance of the tube based on the tactile feeling from the catheter and thus senses curved parts, narrow parts and obstacles in the passageway. This allows the doctor to determine the advancing direction of the catheter, The doctor needs to be experienced and must sometime use his or her instincts in manipulating the catheter's distal end. Further, judging the direction of the insertion pressure is often difficult.
To solve the above drawback, it has been proposed that a sensor be mounted on the distal end of a tube for detecting the magnitude and direction of pressure applied to the sensor by contact of the sensor and the passage way's inner wall.
Japanese Unexamined Patent Publication No. 6-190050 discloses a medical device having a sensor mounted on the distal end of the tube. The sensor of this publication, which is shown in FIG. 17, includes a flexible tube 101 and a plurality of strain gauges provided on the periphery of the tube's distal end. The tube 101 has a plurality of beams 102 and slits 103 at its distal end. The strain gauges are provided mostly on the beams 102. Contacting the sensor against the inner wall of an intra-corporeal passageway deforms the beams 102. This causes the strain gauges to issue signals in accordance with impedance based on the deformation of the beams 102. The magnitude and the direction of the pressure applied to the tube's distal end are measured based on the signal. The doctor determines the advancing direction of the tube by monitoring the measurement results. Determining the advancing direction of the tube is thus facilitated.
However, since the above described strain gauge type sensor has minuscule beams and slits, the manufacturing of the sensor is complicated. This structure is also disadvantageously large.
Further, having projections and recesses as shown in FIG. 17, the sensor's distal end often gets snagged even when advancing in a straight passageway. This may develop a thrombus in the passageway.